* configure.in: Check for unistd.h.

* configure.in: Check for unistd.h.
* configure: Regenerated.

* command.c, cp-valprint.c, fork-child.c, i386-tdep.c,
i386b-nat.c, inflow.c, main.c, maint.c, objfiles.c, solib.c,
source.c, stack.c, symfile.c, top.c, utils.c: Include strings.h
and/or unistd.h to bring prototypes into scope.